Flow Crossover during Collisionless Magnetic Reconnection: A Particle-Labelling Particle-in-Cell Study

During 2D magnetic reconnection, plasma is normally understood to flow from one of the inflow sides into the diffusion region and then turn sharply and join the outflow on the same side. Using particle-in-cell simulations with a modification to allow us to label ions and electrons by their initial locations, we find that inflowing plasma does not join the outflow on the same side; instead, plasma crosses to the other inflow side before changing direction to produce an outflow jet. Furthermore, we find that ions and electrons undergo different crossover mechanisms leading to different crossing patterns. The ion crossover occurs more locally within the ion diffusion region whereas the electron crossover occurs over a wider region as its mechanism does not require electrons to pass through the electron diffusion region. This flow crossover occurs both in symmetric reconnection and in a more complex scenario such as a guide-feld asymmetric reconnection, suggesting that it is a general feature of collisionless magnetic reconnection. Recognizing the existence of the flow crossover can be important in improving our understanding of reconnection in many situations. This research has been partially supported by Thailand's National Science and Technology Development Agency (NSTDA): High-Potential Research Team Grant Program (N42A650868), grant MRG6180176 from Thailand Science Research and Innovation, and by a grant from Kasetsart University Research and Development Institute.